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Features of waffle raft slabs

The features of waffle raft slabs include the following:

  • they are used on flat sites
  • they are wholly above ground
  • no beam excavation is required
  • no controlled or rolled fill is used
  • cardboard slab panel/void formers are used
  • slab panels are on 1 metre grids (approximately)
  • trench mesh or individual bars can be used
  • slab thickness is 85 mm
  • internal beams are 110 mm wide
  • there is minimal concrete volume
  • no beam down drag from clay (above ground slab) occurs
  • shrinkage of slab is lower than stiffened rafts and footing slabs
  • they use 30% less concrete than a stiffened raft
  • they use 20% less steel than a stiffened raft.

This construction is rarely used on Class A and Class S sites.